1. End Show Slide 1 of 36 Biology Earth History Oparin Hypothesis Mr. Karns

2. End Show Slide 2 of 36 17-2 Earth's Early History

3. End Show 17-2 Earth's Early History Slide 3 of 36 Formation of Earth Hypotheses about Earth’s early history are based on a relatively small amount of evidence. Gaps and uncertainties make it likely that scientific ideas about the origin of life will change.

4. End Show 17-2 Earth's Early History Slide 4 of 36 Formation of Earth Evidence shows that Earth was not “born” in a single event. Pieces of cosmic debris were probably attracted to one another over the course of 100 million years. While Earth was young, it was struck by one or more objects, producing enough heat to melt the entire globe.

5. End Show 17-2 Earth's Early History Slide 5 of 36 Formation of Earth Once Earth melted, its elements rearranged themselves according to density. The most dense elements formed the planet’s core. Moderately dense elements floated to the surface, cooled, and formed a solid crust. The least dense elements formed the first atmosphere.

6. End Show 17-2 Earth's Early History Slide 6 of 36 What substances made up Earth's early atmosphere? Formation of Earth

7. End Show 17-2 Earth's Early History Slide 7 of 36 Formation of Earth Earth's early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.

8. End Show 17-2 Earth's Early History Slide 8 of 36 Formation of Earth Scientists infer that about four billion years ago, Earth cooled and solid rocks formed on its surface. Millions of years later, volcanic activity shook Earth’s crust. About 3.8 billion years ago, Earth’s surface cooled enough for water to remain a liquid, and oceans covered much of the surface.

9. End Show 17-2 Earth's Early History Slide 9 of 36 The First Organic Molecules Could organic molecules have evolved under conditions on early Earth? In the 1950s, Stanley Miller and Harold Urey tried to answer that question by simulating conditions on the early Earth in a laboratory setting.

10. End Show 17-2 Earth's Early History Slide 10 of 36 What did Miller and Urey's experiments show? The First Organic Molecules

11. End Show 17-2 Earth's Early History Slide 11 of 36 The First Organic Molecules Miller and Urey’s Experiment Mixture of gases simulating atmosphere of early Earth Condensation chamber Spark simulating lightning storms Water vapor Liquid containing amino acids and other organic compounds Cold water cools chamber, causing droplets to form.

12. End Show 17-2 Earth's Early History Slide 12 of 36 The First Organic Molecules Miller and Urey's experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth. Although their simulations of early Earth were not accurate, experiments with current knowledge yielded similar results.

13. End Show 17-2 Earth's Early History Slide 13 of 36 The Puzzle of Life's Origin Evidence suggests that 200–300 million years after Earth had liquid water, cells similar to modern bacteria were common.

14. End Show 17-2 Earth's Early History Slide 14 of 36 The Puzzle of Life's Origin Formation of Microspheres In certain conditions, large organic molecules form tiny bubbles called proteinoid microspheres. Microspheres are not cells, but they have selectively permeable membranes and can store and release energy.

15. End Show 17-2 Earth's Early History Slide 15 of 36 The Puzzle of Life's Origin Hypotheses suggest that structures similar to microspheres might have acquired more characteristics of living cells.

16. End Show 17-2 Earth's Early History Slide 16 of 36 The Puzzle of Life's Origin Evolution of RNA and DNA How could DNA and RNA have evolved? Several hypotheses suggest: Some RNA sequences can help DNA replicate under the right conditions. Some RNA molecules can even grow and duplicate themselves suggesting RNA might have existed before DNA.

17. End Show 17-2 Earth's Early History Slide 17 of 36 The Puzzle of Life's Origin RNA and the Origin of Life Abiotic “stew” of inorganic matter Simple organic molecules RNA nucleotides RNA able to replicate itself, synthesize proteins, and function in information storage DNA functions in information storage and retrieval RNA helps in protein synthesis Proteins build cell structures and catalyze chemical reactions

18. End Show 17-2 Earth's Early History Slide 18 of 36 Free Oxygen Microscopic fossils, or microfossils, of unicellular prokaryotic organisms resembling modern bacteria have been found in rocks over 3.5 billion years old. These first life-forms evolved without oxygen.

19. End Show 17-2 Earth's Early History Slide 19 of 36 Free Oxygen About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans. Next, oxygen gas accumulated in the atmosphere.

20. End Show 17-2 Earth's Early History Slide 20 of 36 Free Oxygen What occurred when oxygen was added to Earth's atmosphere?

21. End Show 17-2 Earth's Early History Slide 21 of 36 Free Oxygen The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration.

22. End Show 17-2 Earth's Early History Slide 22 of 36 Origin of Eukaryotic Cells What hypothesis explains the origin of eukaryotic cells?

23. End Show 17-2 Earth's Early History Slide 23 of 36 Origin of Eukaryotic Cells The Endosymbiotic Theory The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms.

24. End Show 17-2 Earth's Early History Slide 24 of 36 Origin of Eukaryotic Cells Endosymbiotic Theory Mitochondrion Aerobic bacteria Nuclear envelope evolving Ancient Prokaryotes Plants and plantlike protists Primitive Photosynthetic Eukaryote Primitive Aerobic Eukaryote Ancient Anaerobic Prokaryote Chloroplast Animals, fungi, and non-plantlike protists Photosynthetic bacteria

25. End Show 17-2 Earth's Early History Slide 25 of 36 Origin of Eukaryotic Cells About 2 billion years ago, prokaryotic cells began evolving internal cell membranes. The result was the ancestor of all eukaryotic cells. According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several different prokaryotes.

26. End Show 17-2 Earth's Early History Slide 26 of 36 Origin of Eukaryotic Cells Ancient Anaerobic Prokaryote Nuclear envelope evolving Aerobic bacteria Ancient Prokaryotes

27. End Show 17-2 Earth's Early History Slide 27 of 36 Origin of Eukaryotic Cells Prokaryotes that use oxygen to generate energy- rich molecules of ATP evolved into mitochondria. Mitochondrion Primitive Aerobic Eukaryote

28. End Show 17-2 Earth's Early History Slide 28 of 36 Origin of Eukaryotic Cells Primitive Photosynthetic Eukaryote Chloroplast Photosynthetic bacteria Prokaryotes that carried out photosynthesis evolved into chloroplasts.

29. End Show 17-2 Earth's Early History Slide 29 of 36 Sexual Reproduction and Multicellularity Most prokaryotes reproduce asexually. Asexual reproduction: yields daughter cells that are exact copies of the parent cell. restricts genetic variation to mutations in DNA. Sexual Reproduction and Multicellularity

30. End Show 17-2 Earth's Early History Slide 30 of 36 Sexual reproduction shuffles genes in each generation. In sexual reproduction: offspring never resemble parents exactly there is an increased probability that favorable combinations will be produced there is an increased chance of evolutionary change due to natural selection Sexual Reproduction and Multicellularity

31. End Show - or - Continue to: Click to Launch: Slide 31 of 36 17-2

32. End Show Slide 32 of 36 17-2 Which of the following gases was probably NOT present in the early Earth’s atmosphere? a.hydrogen cyanide b.oxygen c.nitrogen d.carbon monoxide

33. End Show Slide 33 of 36 17-2 Miller and Urey's experiment was a simulation of Earth's early a.volcanic activity. b.formation. c.atmosphere. d.life.

34. End Show Slide 34 of 36 17-2 Proteinoid microspheres are different from cells because microspheres a.have selectively permeable membranes. b.do not have DNA or RNA. c.have a simple means of storing and releasing energy. d.separate their internal environment from the external environment.

35. End Show Slide 35 of 36 17-2 The hypothesis that RNA sequences appeared before DNA sequences a.has some evidence in its favor but is still being tested. b.has been rejected since DNA is required to make RNA. c.has been proven since RNA has been made in laboratories. d.has been rejected because it is illogical.

36. End Show Slide 36 of 36 17-2 As concentrations of oxygen rose in the ancient atmosphere of Earth, organisms began to evolve a.anaerobic pathways. b.plasma membranes. c.metabolic pathways that used oxygen. d.photosynthesis.

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